Floor tile calculator
How many boxes of floor tiles a room needs, from the floor's area and what one box covers.
How the number is worked out, a worked example and questions
How the number is worked out
- Measure the floor. The length times the width, in metres, is the area in square metres. A room that is not a rectangle can be drawn, and the area comes from the drawing.
- Add the allowance for cuts. The planner starts at 10%, a labelled example. Change it to suit your tile and how it is laid.
- Divide by what one box covers. The square metres printed on the box you are buying.
- Round up to whole boxes. Always up, even when the sum is only just over a whole number.
- Count the adhesive and grout from the bag. Enter what one bag of each covers, from the bag. The bags are counted for the floor's area, without the allowance for cuts. Left blank, each line shows the area to cover and is marked Check first.
The list then adds what a tiled floor needs besides the tiles. What the tiles go onto comes from your answer about the floor: tile backer board or overlay ply on a timber floor, and a flat, dry floor to tile on for any other. Then tile spacers or levelling clips, sanitary silicone sealant for the edge of the floor, a threshold or door bar for each doorway, the tiling tools, and knee pads, gloves, safety glasses and a dust mask. Each is marked Need or Check first. No underlay or damp-proof membrane is listed, because tiles are stuck down and not floated.
A worked example
A room 4.2 m by 3.6 m with a tiled floor, with 10% added for cuts. One box covers 1.44 m² and the other covers 2 m². Adhesive is entered at 4 m² a bag and grout at 6 m² a bag. These are example figures, not a product.
| Working | 1.44 m² boxes | 2 m² boxes |
|---|---|---|
| Floor area | 15.12 m² | 15.12 m² |
| With 10% for cuts | 16.632 m² | 16.632 m² |
| Boxes to buy | 12 boxes | 9 boxes |
| Tiles in those boxes | 17.28 m² | 18 m² |
| Left over | 0.648 m² | 1.368 m² |
The box size changes the count: 12 boxes of one and 9 boxes of the other for the same floor. The adhesive and grout are counted for the floor's 15.12 m², without the allowance: 4 bags of adhesive and 3 bags of grout. The 4 m² and 6 m² are example figures too.
The planner counts boxes by area. The box's label says how many tiles it holds, so multiply the boxes by that number to count the tiles.
Mistakes that cost a box
- Leaving out the allowance for cuts. In the example the bare floor area divided by 1.44 m² says 11 boxes. The room needs 12 boxes.
- Working from the tile's size. The size of one tile does not say how many are in the box. Use the square metres printed on the box you are buying.
- Rounding down. A box is sold whole, so a shortfall, however small, needs the next whole box.
- Keeping 10% for a diagonal or herringbone layout. Those lose more in cuts, and so do large tiles in a small room. Raise the allowance.
- Buying boxes from different batches. The shade can differ between batches. The box shows the batch.
Questions
How many boxes of floor tiles for a 4.2 m by 3.6 m room?
With boxes that cover 1.44 m² and 10% extra for cuts, 12 boxes. The floor is 15.12 m², which is 16.632 m² with the extra. With boxes that cover 2 m² it is 9 boxes.
How much extra should I add for cuts?
The planner starts at 10%, a labelled example and not a standard. A diagonal or herringbone layout, large tiles in a small room or an awkward floor needs more. The tile's own fitting guide comes first.
Which box size does it start with?
A box that covers 2 m², with 10% extra for cuts. They are labelled examples, not a product. Change them to the figures on your box.
Does it count adhesive and grout?
Yes, if you enter what one bag covers, from the bag. That figure depends on the tile size, the trowel and the joint width, so the planner has none of its own. Without it the line shows the area to cover and says what to check.
What do the tiles go onto?
The planner asks what the floor is going on to. A timber floor flexes, and tiles crack on a floor that moves, so the list has tile backer board or overlay ply. On concrete or screed it has a flat, dry floor to tile on. Either line is marked Check first: the adhesive's and the board's instructions decide.
What if the room is not a rectangle?
Draw it. Tap each corner, or start from an L and type each wall. The floor area comes from the drawing, so an L-shaped room or one with an alcove is counted whole.